Tubular water quench apparatus with water film cooling

ABSTRACT

Film of an organic thermoplastic polymer is manufactured by drawing an extruded, inflated, hot, tubular film from an extruder and passing the film into contact with layers of cooling liquid supported by symmetrically disposed collapsing elements adapted to effect a partial but not complete collapse of the tubular film to the lay flat form, cooling liquid being simultaneously supplied to a plurality of locations distributed over the surfaces of the collapsing elements at a rate sufficient to maintain layers of cooling liquid thereon.

United States Patent 9 Van Kralingen Aug. 21, 1973 TUBULAR WATER QUENCHAPPARATUS WITH WATER FILM COOLING [75] Inventor: Peter 11. VanKralingen,

Delft, Netherlands [73] Assignee: Shell Oil Company, New York,

[22] Filed: Jan. 20, 1972 [21] Appl. No.: 219,278

Related US. Application Data [62] Division of Ser No. 849,849, Aug. 13,1969, Pat. No.

[30] Foreign Application Priority Data Dec. 31, 1968 Great Britain61,899/68 [56] References Cited UNITED STATES PATENTS 7/1951 Bailey264/95 12/1958 Buteux et al 425/71 3,243,486 3/1966 Pilaro 264/953,543,334 12/1970 Sudo 425/71 3,551,540 12/1970 Pellicciari et a1.425/66 X 3,274,313 9/1966 Harp, Jr 264/95 X 3,275,723 9/1966 Cappuccio264/70 3,296,661 1/1967 Moustier 264/95 X 3,539,669 11/1970 Chein-Ho264/178 R Primary Examiner-Robert L. Spicer, Jr. Attorney-Joseph W.Brown et a1.

[ 5 7] ABSTRACT Film of an organic thermoplastic polymer is manufacturedby drawing an extruded, inflated, hot, tubular film from an extruder andpassing the film into contact with layers of cooling liquid supported bysymmetrically disposed collapsing elements adapted to effect a partialbut not complete collapse of the tubular film to the lay flat form,cooling liquid being simultaneously supplied to a plurality of locationsdistributed over the surfaces of the collapsing elements at a ratesufficient to maintain layers of cooling liquid thereon.

5 Claims, 10 Drawing Figures Patented Aug. 21, 1973 3,753,633

2 Sheets-Sheet l Patented Aug. 21, 1973 3,753,633

2 Sheets-Sheet 2 FIG. l0

TUBULAR WATER QUENCH APPARATUS WITH WATER FILM COOLING This is adivision, of application Ser. No. 849,849, filed Aug. 13, 1969 now US.Pat. No. 3,700,763.

The present invention is concerned with the manufacture of films fromorganic thermoplastic polymers, for example, polypropylene by a process(hereinafter referred to as a process of the kind defined) in which anintemally-blown film is extruded continuously and in a dwonwarddirection from an organic thermoplastic polymer melt and the resultingblown tube or bubble is cooled and flattened to lay-flat form. Thepresent invention is also concerned with the resulting films in layflatform or slit into sheets, tapes, ribbons or filaments.

It is known to employ water as a cooling medium in processes of the kinddefined above. Many proposals have been made in regard to the manner inwhich the blown tube is brought into contact with the cooling water. Forexample, the use of a water bath has been proposed. However, the processof this proposal is difficult to control and produces a poor clarityproduct'unless special techniques such as described in U.S. PatentApplication Ser. No. 710,566, Chien-Ho, are employed. Another methodbased on the concept of a water cascade on the outer surface of theblown tube has also been proposed. But this method also hasdisadvantages such as film size limitations. There is also a tendencyfor variations in the film cooling efficiency occuring with smallchanges in the film tube diameter. The cascade can be formed by passingthe blown tube through a fixed guide means such as a ring or tubeprovided, for example, with an annular water trough. The wateroverflowing from the trough passes down the outer surface of the blowntube as an enveloping curtain or "cascading column. The curtain orcolumn can be wholly or mainly exposed to the surrounding atmosphere asin the case of the method described, for example, in UK. Pat. Nos.876,460 and 872,115 in which the cooling water is supplied by one ormore annular rings through which the blown tube passes. Alternatively,the curtain or cascading column of water can be confined within theannular space formed between the outer surface of the blown tube and theinner surface of a cylindrical metal tube through which the blown tubepasses as in the case of the method described, for example, in UK.Patent Nos. 853,745 and 741,963. The cooling water can also be suppliedby sprays surrounding the top of the blown tube in place of theaforesaid annular trough. in anotehr approach to the problem ofeffecting adequate cooling of the blown tube, the lattter is passedthrough a water bath while its interior surface is cooled by contactwith an internal, smooth-surfaced cooling mandrel. Such a technique isdescribed, for example, in UK. Patent Nos. 1,061,342 and 1,043,933. Theconcept of cooling the interior of the blown tube with a water curtainor cascade has also been proposed but inevitably this leads tocomplications in both the design of the equipment and in the operationthereof.

In general, water cooling techniques involving the use of an annularring or tube through which the internally-blown tube must pass sufferthe disadvantage of lack of flexibility in regard to the size of theblown tube which can be handled. To be effective the ring or tube mustprovide an even water cascade or curtain over the whole of the outersurface of the blown tube. In prac tice this usually means that aparticular equipment can produce only one size of blown tube. Moreoverlittle or no variation in blown tube diameter can be tolerated duringthe operation of the equipment.

Other important factors arise in the operation of any equipment in whichcooling is effected by means of a water curtain or cascade on theexternal and/or internal surface(s) of blown tube. For example, an evencooling over the whole surface of the blown tube is essential not onlyin order to maintain stability of the blown tube but also to avoidoptical variations in the resulting thermoplastic film. Also, when thecooling water is applied to the blown tube by means of sprays whichexert pressure on the external surface thereof particular care must betaken to avoid localized concavities or convexities which can arise fromlocal variations in the water pressure over the tube surface. With anyof the methods hitherto proposed for supplying the cooling water to theblown tube the maintenance of an enveloping cascade or curtain ofcooling water of the same water thickness round the whole circumferenceof the blown tube can be difficult. This is particularly so when theblown tube passes through a surrounding metal tube of significant depthwithin which local hot spots can easily develop due to localizedthinning of the water film.

The present invention is based on a new approach to the cooling problemin which the blown tube is pressed against supported water films solelyby the fluid pressure within the blown tube. The blown tube is therebyboth cooled and pratially flattened under conditions which result ineven cooling and even pressure over the entire water-cooled surface. Thewater films are supported in such a manner that within relatively widelimits blown tubes of any diameter can be handled. Minor variations inthe diameter of the blown tube which occur from time to time duringoperation of the process have substantially no effect on the opticalproperties of the resulting film or on the stability of the blown tubeitself or on the cooling efficiency of the process.

According to the present invention a process of the kind defined for themanufacture of film from a thermoplastic organic polymer, comprisesdrawing an extruded, inflated, hot, tubular film from an extruder andpassing the hot tubular film into contact with layers of cooling liquidsupported by symmetrically disposed collapsing elements adapted toeffect a partial but not complete collapse of the tube to the lay-flatform, cooling liquid being supplied simultaneously to a plurality oflocations distributed over the surfaces of the collapsing elementsthrough a plurality of apertures or channels in the walls of thecollapsing elements at a rate sufficient to maintain the layers ofcooling liquid thereon. The present invention also includes theresulting film.

The present invention also includes apparatus for cooling an extruded,inflated, hot, tubular film of an organic thermoplastic polymer duringthe manufacture of film by a process of the kind defined. The apparatuscomprises a pair of collapsing elements adapted to effect a partial butnot complete collapse of a hot inflated film to the lay-flat form, eachof collapsing elements being provided with means for supplying a coolingliquid simultaneously to a plurality of locations distributed over thesurface thereof through a plurality of apertures or channels in the wallof the collapsing element in such a manner that a layer of coolingliquid can be maintained on the surface.

Although not limited in regard to the shape and nature of collapsingelements used, the process of the present invention will usually employtwo such elements. The general shape and symmetrical disposition withrespect to the blown tube of such collapsing elements can be generallysimilar to the collapsing boards or frames well known in the filmmanufacturing and processing art, but other forms of collapsing elementscan be used. Usually the cooling liquid will be water. Preferably thecollapsing elements are used in combination elements. The partiallycollapsed blown tube is led into the bath and between nip rollersdisposed therein which effect a complete collapse of the blown tube tothe lay-flat form. Preferably the collapsing elements are disposed so asto provide guiding surfaces which support the partially collapsed blowntube as it enters the cooling liquid bath in order to prevent wrinlkingor marking thereof.

Advantageously the collapsing elements are made from porous metal, thepores constituting a multiplicity of apertures in the walls thereof. Insuch cases porous metal plates of any suitable shape can be employed.Cooling liquid can be supplied thereto by providing a water chamber (oreven a plurality of separate inlet ports) at the rear of the plates. Thechamber extends over part or all of the rear surface therof.Alternatively, plates having a plurality of channels or grooves in thesurface thereof or having a number of spaced apertures of anyconventional shape, opening into said surface, for example, circularholes can be used in place of porous metal plates. The collapsingelements can be flat plates or plates shaped in the direction of filmtravel so as to provide support for the curved lower part of the blowntube. The elements can also be at right angles so as to correspond tothe shape of the lower part of the blown tube at its line of firstcontact with the collapsing elements. Porous or apertured rollers canalso be used as collapsing elements. Alternatively, each collapsingelement can comprise a box-like structure having a plurality of freelyrotatable rollers disposed in longitudinal slots in one surface thereofso as to project slightly therefrom. The rollers rotate with clearancein the slots so as to permit cooling liquid to flow from the hollowinterior of the collapsing element onto the surfaces of the rollers andonto those portions of the surface of the collapsing element which liebetween the rollers. If desired, the collapsing elements may be joinedby side portions where the elements come close together at their loweredges to effect cooling of the two opposed side portions of the blowntube which otherwise might not contact the collapsing elements.

The process of the present invention provides for an even water coolingof a downwardly-extruded blown film by means of water layers in whichthe water flow is parallel to the direction of movement of the film. Atthe same time a partial flattening of the blown tube is achieved bymeans of symmetrically disposed collapsing elements. Usually thispartial collapse of the blown tube will be such that the tube is broughtquite near to the lay-flat form. Preferably the line of first contactbetween the blown tube and each of the collapsing elements approximatesa horizontal line over as much as possible of the tube 's length. Thismay be achieved by suitably shaping the tube-contacting surface of eachof the collapsing elements in the manner described herein.

The present invention can be applied to the manufacture of film from anythermoplastic organic polymer which is suitable, in regard to softeningpoint and melt stability, for use in a process of the kind defined.Suitable thermoplastic organic polymers include, for example, polyvinylchloride, polyesters, nylons and polyolefins. The present invention isparticularly applicable to crystalline polymers, for example the nylonsand polyolefins. The term polyolefin is used herein to include an olefinpolymer or copolymer as such and also a polymer composition the majorpart of which is polyolefin or mixture thereof. Examples of polyolefinswhich can be used in carrying out the process of the present inventionare polyethylene and polypropylene. The present process is particularlysuitable for the manufacture of high clarity polypropylene film havinggood physical properties.

It is a particular advantage of the invention that various widths andthicknesses of film can be manufactured at high throughput rates withthe same cooling unit, and in general blow-up ratios in the range of 0.1to 2.0 can be employed.

The present invention will be further described with reference to theaccompanying diagrammatic drawings in which:

FIG. I is a schematic drawing showing a general arrangement for filmmanufacture in accordance with the present invention,

FIGS. ll-Vlll are schematic representations showing various forms ofplate-like collapsing elements,

FIG. [X is a schematic drawing showing an alternative form of collapsingelement, and

FIG. X is a schematic representation showing the use of collapsingelements in the form of porous rollers.

Referring to FIG. I, a hot blown tube 11 of, for example, polypropyleneis extruded downwardly from an extruder die 12 of conventional form andis cooled, in accordance with the present invention, by means of acooling unit comprising a pair of porous plates 13, 14 which constitutethe collapsing elements and a body of cooling water contained in a tank15. The plates 13, 14 also effect a partial collapse of the blown tube 11, complete collapse to the lay-flat form being achieved by drivennipping rollers 16, 17 located within the cooling water in the tank 15.These nipping rollers 16, 17 also serve to draw down the blown tube 11from the extruder die 12. The lay-flat film is removed over a roller 18by conventional haul-off equipment (not shown). Each of the porousplates 13, 14 comprises a thin hollow box having a porous front surface130, 14a adapted to contact the blown film, and an inlet pipe 19, 20 forsupplying water under pressure to the interior of the box. In operationthe water in the interior of the box permeates to the front surface or14a through the pores thereof to form a layer of cooling liquid on thesurface 13a or 14a. The size of the pores is such that under the waterpressure employed an adequate thin layer of cooling water is maintainedon the surfaces 131 and during operation of the cooling unit. Thecooling water can be supplied to the collapsing elements at ambienttemperature, for example at 10 to 20C, and its rate of supply should besuch that thin layers of water are maintained over the whole surfacethereof during operation of the process.

Referring to FIGS. I! to VIll, FlG. II shows a collapsing element in theform of a plate 21 having a large plurality of convex protuberances 22,all of the same size and shape, on its surface. The spaces between theprotuberances 22 provide channels for the supply of cooling liquid tothe whole surface of the plate 21, the liquid being supplied from thetop of the plate. FIG. III shows a collapsing element in the form of ahollow box 23 having an apertured front surface containing a number ofdiamond-shaped apertures through which cooling water can be supplied.FIG. IV shows a somewhat similar collapsing element in which theapertures comprise slits 24. FIG. V and VI show porous plate collapsingelements which are shaped in the direction of travel of the blown tubeto provide additional guidance and support for the blown tube. FIG. VIIshows a porous plate collapsing element which is shaped at right anglesto the direction of travel of the blown tube in order to straighten theline of first contact of the blown tube with the collapsing elements. Aswill be apparent from FIG. I this line of first contact (shown dotted atA) tends to be parabolic in form when the plates have a flat surface.

The present invention can be illustrated by the following example:

EXAMPLE Polypropylene film was manufactured in accordance with theprocess described with reference to FIG. I of the accompanying drawings,the collapsing elements comprising porous plates each shaped to providea downwardly and inwardly extending flat surface 40 centimeters inlength for partially collapsing, and cooling, the blown tube and a flatvertical portion forming a guide for the film as it entered the waterbath. The bottom edge of this vertical portion was therefore below thewater surface, and the two plates were disposed so that their respectivevertical portions were 2 millimeters apart. The collapsing portion ofeach of the collapsing elements was at an angle of 160 to the verticaland the mid-part of each collapsing element lying between the collapsingportion and the vertical portion was curved, the radius of curvaturebeing 12.5 centimeters. The water level in the tank was just below thisradiused mid-part of the collapsing elements. The collapsing elementscomprised sheets of porous copper material. Cooling water was suppliedthereto by water chambers welded to the back of the plates and coveringthe upper part of the rear surfaces thereof. The polypropylene wasextruded downwardly in conventional manner. In a number of runs theblow-up ratio was varied to produce films of various widths, with filmthicknesses of 30, 50 and microns. Using a 200 millimeter diameterannular extrusion die and operating at a melt temperature of 240C,polypropylene films of good optical and mechanical properties wereobtained under the following conditions:

Cooling water input temperature 15C Cooling water supply rate (to bothcollapsing elements) 5 liters per minute Blow-up ratios 0.4; 0.6; 0.8;1.2

Film production speed 15, 3O meters/minute I claim as my invention:

1. An apparatus for cooling an extruded, inflated, hot, tubular film ofan organic thermoplastic polymer, said apparatus comprising a pair ofopposed symetrically disposed plate-like collapsing elements which arearranged so that the tubular film comes into initial liquid quenchingocntact solely by pressure within the tubular film and which collapsingelements are adapted to effect a partial but not complete collapse ofsaid hot inflated film prior to entering a pair of nip rolls, each ofsaid collapsing elements being provided with means for supplying acooling liquid simultaneously to a plurality of locations distributedover the surface thereof in such a manner that a layer of cooling liquidis maintained on said surface.

2. An apparatus as claimed in claim 1 wherein said collapsible elementscomprise porous metal plates said pores constituting a multiplicity ofapertures in the walls thereof in combination with a water chamber atthe rear of said plates and extending over part or all of the rearsurface thereof.

3. An apparatus as claimed in claim 1 wherein said collapsible elementscomprise plates having a plurality of channels or grooves in the surfacethereof.

4. An apparatus as claimed in claim 1 in combination with a coolingliquid bath and nipping rollers disposed within said bath to effect acomplete collapse of said partially collapsed film.

5. An apparatus as claimed in claim 4 in which when said bath containscooling liquid said collapsing elements are disposed within said bath soas to provide guiding surfaces which support said partially collapsedfilm as it enters said cooling liquid in order to prevent wrinkling ormarking of said film.

l f f F

2. An apparatus as claimed in claim 1 wherein said collapsible elementscomprise porous metal plates said pores constituting a multiplicity ofapertures in the walls thereof in combination with a water chamber atthe rear of said plates and extending over part or all of the rearsurface thereof.
 3. An apparatus as claimed in claim 1 wherein saidcollapsible elements comprise plates having a plurality of channels orgrooves in the surface thereof.
 4. An apparatus as claimed in claim 1 incombination with a cooling liquid bath and nipping rollers disposedwithin said bath to effect a complete collapse of said partiallycollapsed film.
 5. An apparatus as claimed in claim 4 in which when saidbath Contains cooling liquid said collapsing elements are disposedwithin said bath so as to provide guiding surfaces which support saidpartially collapsed film as it enters said cooling liquid in order toprevent wrinkling or marking of said film.